Nanoimprint lithography is a method of fabricating nanometer scale patterns by mechanical deformation of imprint resist and subsequent processing. The imprint resist can be a thermally softened or photo-initiated liquid coating that is cured by heat or UV light during the imprinting. A template is brought into contact with the liquid and the liquid is cured. The cured liquid includes an imprint of any patterns formed in the template. Alignment of the template with the substrate is performed prior to curing the liquid as described in U.S. Pat. No. 6,916,584. Adhesion between the resist and the template must be controlled to allow proper release, U.S. Pat. No. 7,157,036.
A nano-pattern “parent” is produced using lithography on a silicon or glass parent. The parent pattern, sometimes called a positive image, is created using durable or environmentally stable materials, for example, a chrome positive created on glass. The pattern is then replicated on a liquid Polydimethylsiloxane (PDMS) layer, sometimes called a child layer or negative image. The PDMS is then cured. The final image is used as a template or stamp to reproduce the image on multiple products. The PDMS child pattern is then replicated onto another liquid layer, for example an epoxy-based negative photoresist (SU-8), re-creating the original positive image. Su-8 can be hardened using a combination of light and heat.
Various techniques can be used for making the pattern transfer from the parent pattern to the child template. For example U.S. Pat. No. 8,420,124 teaches a contact molding technique and U.S. Pat. No. 7,704,425 teaches an imprint method. The resulting stamp, made from an elastic polymer, is known to be compliant. The compliance can be useful for example, to bend the stamp when it is applied to a substrate for pattern transfer in order to eliminate trapped air and ensure a good contact with the photoresist surface as discussed in U.S. Pat. No. 7,363,854. U.S. Pat. No. 7,140,861 teaches attaching the elastomeric stamp to a rigid transparent substrate to allow the substrate to control the bending of the stamp into an arc. Wilhelm (Thesis, Massachusetts Institute of Technology, June 2001) teaches casting the stamp around spring steel. As a result of the stresses, however, and under repeated bends, separation of the elastomer from the substrate or steel will occur resulting in waste and short life for the template.
Despite the good properties of PDMS, there is a possibility of mechanical stress and thermal expansion causing errors in the moldable layer. As a result, U.S. Pat. No. 7,704,425 teaches performing all processing steps when using the stamp to transfer a pattern to a substrate at a constant control temperature, which is inconvenient in a manufacturing environment.
What is needed is a simple means to make a reinforced elastomeric template or stamp that is easy to mount either flat or with some curvature. It must also be resistant to mechanical stress and thermal expansion and have excellent durability. Finally, for UV curing during the pattern transfer process, the stamp must pass light even with the reinforcing substrate in place.